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Kentaro is an incredibly muscular man, having apparently trained his entire life. He has short, spiky black hair, bushy eyebrows, and after training Rintaro for ten years has grown a similarly unkempt beard. He has only ever been seen wearing a white gi with the sleeves torn off at the shoulders.[2]

Kentaro has been shown to care greatly for his son, taking him out to the amusement park when Rintaro was just a boy, and showed concern for Rintaro's well-being after the boy suffered his first incident due to his Hentai Syndrome. His dedication goes as far as to train his son for ten years in order to overcome this ordeal, and was glad to hear Rintaro's determination to be strong like him.[3]

His personality is shown to be quite strong-willed and is the inspiration for Rintaro's determination, not only to cope with the Hentai Syndrome, but also in his academic studies. In his own words, "A Real Man Strives to be at the Center." This is what drove Rinataro to obtain the highest scores during the mid-term exams.

While out at an amusement park with his son, Kentaro warns him to not run so much as it's dangerous. Ignoring his father, Rintaro ends up running into a nearby woman's chest, dropping his ice-cream onto her breasts. Telling his son to apologize, Rintaro's father becomes aware of his son's sudden pain. Taking him to the doctor's, they learn that Rintaro carries a disease called Henisei Tashu Ijō Syndrome, or the Hentai Syndrome for short. Distressed that his son was destined to die a virgin, Rintaro's father is forced to knock out Rintaro when the boy was at risk of having another incident due to the doctor's appearance. Asking her to be more careful around his son, Rintaro's father than resolves to teach his son how to handle his condition.[4]

Rintaro and his father at the end of his training.

Taking Rintaro out to the forests of Mount Fuji where he himself had trained as a child, calling it The Quiet Shore Nobody Knows. For the next ten years, he teaches Rintaro in the ways of Ryūha Koei Sōgetsu until his son is ready to enter high school. Warning his son to be prepared for anything, Rintaro impresses his father with the promise to never touch or be touched by a woman.[5]

Koei Ryuha Sōgetsu Master:As the man responsible for training Rintaro to the level of strength he has currently, it can be inferred that Kentaro is capable of similar if not greater feats as well. Due to Kentaro's greater experience, he is able to teach it much better than Rintaro as he is later seen training Rurina.[6]

Immense Strength: As evidenced by his muscular body, Kentaro has incredible strength where he was able to split apart the land itself when making a line to keep Ayane and Rurina away from Rintaro with one punch.

Immense Speed and Reflexes: Kentaro also possesses extremely high speed and reflexes being able to make the attack that created the line between Ayane, Rurina, Rintaro, and himself before any one of them managed to react despite all three of them having powerful speed themselves.